One-particle excitations in strong-coupling superconductors: A new realization of the t-J model

We study the one-particle excitations in strong-coupling superconductors described by a negative-U Hubbard Hamiltonian. We show that the problem of single-particle excitation can be mapped onto that of a hole in a polarized antiferromagnetic Heisenberg model. We discussusing a self-consistent diagrammatic approachthe distortion of the superfluid order parameter in the vicinity of the quasiparticle and the connection with the pairing-bag problem.